For the Pesto
For pesto, pulse all ingredients in a food processor until smooth (adding water if need to make smooth) and season to taste. Chill until ready to serve (but pull from fridge an hour before serving).
For the Courgette Flowers
For courgette flowers, stir ricotta with Parmesan, basil, garlic and lemon zest and season to taste (double filling recipe if zucchini flowers are large – 3-inches or longer).
Fill a piping bag fitted with a large, plain tip with cheese mixture. Gently wash then dry zucchini flowers on paper towel. To fill, gently open flower, trying not to tear the petals open and pipe in filling. Chill until ready to cook.
For the Batter
Heat oil in a deep pot (or tabletop fryer) to 190°C. Make batter. Whisk all ingredients together immediately before using.
Sprinkle filled flowers lightly with flour and dip in batter. Gently set flower in hot oil, using a slotted spoon and fry for 2–3 minutes, turning once. Remove onto a paper towel to drain.
To serve, spoon a little pesto on a plate and arrange 2 courgette flowers on top. Serve immediately.